Chemistry

Science of Contemporary Issues

Lecture 9

CFCs, Replacements & The Montreal Protocol

Chapman Cycle with Catalyst

The catalyst disrupts the cycle and removes ozone at a faster rate than it can be created

Ok, Where Are the Other Free Radicals?

chlorofluorocarbons

Contain Cl Contain F

Contain C (backbone)

dichlorodifluoromethane methane = CH4

How many valence e− are there in this Lewis structure?

A. 4 B. 8 C. 24 D. 28 E. 32

Where Do The CFCs Come From?

How a Refrigerator Works

Compressor: Cold gaseous refrigerant → Hot liquid refrigerant

Outer Coils: Hot liquid refrigerant → Warm liquid refrigerant

Inner Coils: Warm liquid refrigerant →

Cold gaseous refrigerant

HEATS UP THE HOUSE

COOLS DOWN THE FOOD

BACK SIDE

INSIDE

Refrigerant Gases CFCs

chlorofluorocarbons HCFCs

hydrochlorofluorocarbons

HFCs hydrofluorocarbons

HFOs hydrofluoroolefins

olefins: chemicals with C-C double bonds

 release Cl in stratosphere

 ligher than air  long lifetime (100 yrs)

 shorter lifetime (10 yrs)  less likely to reach

stratosphere

and  zero ozone- destroying potential

 greenhouse gases

 zero ozone-destroying potential  much shorter lifetime (11 d) = less

potent greenhouse gas

Halon Fire Extinguishers Halons are chemicals made of C, Br, and Cl and/or F

that are used in fire extinguishers (the “Cousins” of CFCs)

CBrClF2 (Halon 1211)

CBrF3 (Halon 1301)

• Used by the military and in aircraft • Illegal elsewhere after the Montreal Protocol

 release free radical Br atoms in the stratosphere

Difluoroethane – HFC

boiling point −25 oC

Will this chemical destroy the ozone layer?

C2H4F2

A. Yes, it will cause a lot of damage B. Yes, it will cause medium damage C. No, it does not contain Cl or Br D. No, but it is a greenhouse gas E. I don’t care – I want to know how any of this relates

to the ozone destruction and Chapman Cycle!!

Estimating Ozone Depleting Potential

• Cl or Br atoms in molecule • Long atmospheric lifetime

These properties increase ozone-depleting potential:

• They do not contain Cl or Br • They do not last long in the atmosphere

(they have a short atmospheric lifetime, usually contain C-H bonds and/or C=C bonds)

Molecules will not lead to ozone depletion if:

Discovery of Ozone Depletion!

•

1995 Nobel Prize

Experimental

analyses show that as

ClO• concentrations

increase, ozone

concentration

decreases.

Chapman Cycle with Catalyst

The catalyst disrupts the cycle and removes ozone at a faster rate than it can be created

Here’s Out Catalyst – Ruins Cycle

0

100

200

300

400

500

600 F

-F

O -F

B r-

B r

O -C

l

O -B

r

C l-

C l

C -B

r

O -O

i n

O zo

n e

C -C

l

H -B

r

H -C

l

C -F

O =

O

H -F

B o

n d

S tr

e n

g th

( k

J/ m

o l)

Atoms Connected by Bond

Bond Strengths and Reactivity

weaker bonds than O3 stronger bonds than O3

related to F related to Cl

related to Br O2 or O3

λ ≤ 242 nm

λ ≤ 320 nm

2Cl. + 2O3 2ClO . + 2O2

2 ClO. ClOOCl

The chlorine radical attacks an O3 molecule:

Then two chlorine monoxide radicals combine:

UV photon + ClOOCl ClOO. + Cl.

ClOO. Cl. + O2

The ClOOCl molecule then decomposes:

The net reaction is: 2 O3 3O2

The Cl. radicals

are free to

attack more O3

The Cl. radicals are

both consumed and

generated; they act

as catalysts

Equations of the Catalyst

Why is the Ozone Hole Above Antarctica?

A. Ozone is light, so it floats to the top (north) of the globe

B. The cold air in the Antarctic removes ozone from the stratosphere

C. CFCs are concentrated above Antarctica

D. The Polar Stratospheric Clouds are to blame

E. Something else Ozone hole = Less than 220 DU Has been as low as 100 DU

The North Polar Vortex in Winter 2013

The South Polar Vortex and the Ozone Hole Aug 1 to Oct 8

no data

Seasonal Ozone “Hole”

Polar Stratospheric Clouds (PSCs)

PSCs are thin and made of ice crystals

Polar Stratospheric Clouds (PSCs)

PSCs are thin and made of ice crystals

Section #2 – Stop Here

NOTE: Section #2 Stopped at this slide and if you are in Section #2, we will pick up here on Tuesday!

Section #1 students covered the next slides in Lecture #9

Ozone Measurements From Satellite

2020 Minimum occurred on

October 6 2020:

94 DU

Ozone Hole this Week: 2018, 2019, 2020

LINK https://ozonewatch.gsfc.nasa.gov

Ozone Hole this Week – 2019 & 2020!

LINK https://ozonewatch.gsfc.nasa.gov

The #1 Warm–Up Question Asked:

• Is there any way that ozone can be made (in large amounts) and pumped into the

stratosphere to help the ozone hole?

1/A) Yes, this is possible, but it would be too expensive 2/B) No, this is impossible. We do not know how to make large amounts of ozone 3/C) No, this is impossible. We do not have a way to pump any type of gas up to the stratosphere. 4/D) I have a different idea of why it would not be possible…...

Ground Level (Troposphere) Ozone is Destructive

leaf damaged by ozone ozone damages rubber, lungs, and everything it touches

cracks from

ozone exposure

Humans do not know how to store ozone – it will destroy every container! (Ozonated water is in glass, but will dissipate when exposed to air)

Photons (Wavelength) in UV Spectrum (are the energy to naturally create ozone)

O O

O

O O

O O

O

O

O

O

O

Allotropes

λ ≤ 242 nm

Ozone Generator

wire

wire

O2 O3

Generated ozone is used immediately

Ozone Generators are Used: • To make small amounts of O3 for experiments • To make larger amounts of O3 for water purification

✓ The ozonated water….... kept in glass......

Pumping Ozone to 10,000 km Would Be Difficult and Ineffective

Ozone would just join the cycle, only increasing concentration for a short time

$1,000,000 Question: What would happen to ozone

(if some new, fancy way of transporting it to the south

pole was invented?????

Clicker Question

• This molecule is a __________ ????

A. CFC

B. HCFC

C. HFC

D. HFO

E. Halon

F. None of the above

Estimating Ozone Depleting Potential

• Cl or Br atoms in molecule • Long atmospheric lifetime

These properties increase ozone-depleting potential:

• They do not contain Cl or Br • They do not last long in the atmosphere

(they have a short atmospheric lifetime, usually contain C-H bonds and/or C=C bonds)

Molecules will not lead to ozone depletion if:

Refrigerant Gases & CFC Replacements CFCs

chlorofluorocarbons HCFCs

hydrochlorofluorocarbons

HFCs hydrofluorocarbons

HFOs hydrofluoroolefins

olefins: chemicals with C-C double bonds

 release Cl in stratosphere

 lighter than air  long lifetime (100 yrs)

 shorter lifetime (10 yrs)  less likely to reach

stratosphere

and  zero ozone- destroying potential

 greenhouse gases

 zero ozone-destroying potential  much shorter lifetime (11 d) = less

potent greenhouse gas

And… Halons

(Already existing halons can be recycled into new fire extinguishers)

Halons: Contain Br, C, and can have H, Cl, and/or F

 release Br atoms in stratosphere

CBrClF2 (Halon 1211)

CBrF3 (Halon 1301)

• Used by the military and in aircraft • Illegal elsewhere after the Montreal Protocol

Montreal Protocol

1974

1978

1980

1985

1987

•

1987

Warm-Up Q3 In the year 2000, long after the Montreal Protocol was signed,

only small amounts of CFCs were being produced. However, the

concentration of "effective chlorine" (a measure of Cl, ClO,

and other ozone-destroying chemicals) was at its highest level

in history. How can this be?

Lax emission regulation as well as the massive increase in industrial development in the developing world can account for this.

“…the lifespan of CFCs in the atmosphere can be well over 100 years. Therefore, it was the mass accumulation of the CFCs made from that point and all the time before that…”

A

C

Products that use CFCs are still in use. B

Stratospheric Chlorine Lags Behind CFC Production

Montreal Protocol Signed

CFC production

Quiz Time!

Questions?